Multi-tank ion exchange water treatment system

ABSTRACT

A series of ion exchangers are connected in parallel in a water treatment system and are electrically interlocked against simultaneous regeneration. After an exchanger regenerates, it is held in standby status and is automatically returned to service use when another exchanger begins its regeneration cycle.

United States Patent 1 1 Yocum Apr. 8, 1975 [54] MULTI-TANK [ON EXCHANGEWATER 3.044.626 7/l962 Rose 2lO/l03 TREATMENT SYSTEM 3,366.24! l/l968McMorris 210/96 3,383.3l0 5/1968 Ammer 2l0/96 X [75] In e t C arl s u sll. 3,396,845 8/1968 Bouskill 210/190 x [73] Assignee: Rock Valley WaterConditioning, I

Inc" Rockford "L Primary E.rammer-Roy Lake Asxistun! E.\'aminerCraig R.Feinberg lzzl Flled: 1973 Attorney, Agent, or FirmWolfe, Hubbard,Leydig, 211 App]. No.: 387,115 &

1521 11.5. c1. 210/96; 2l0/98; 210/190 {57] ABSTRACT [51] Int. Cl 801d15/06 A series of ion g rs r n te in parallel in [58] Field of Sear h210/96 93 140 142 19() a water treatment system and are electricallyinter- 2 I0/l9l. I I8, 263, 102 [03, [05 424 locked against simultaneousregeneration. After an exchanger regenerates, it is held in standbystatus and is [56] Ref e (jir d automatically returned to service usewhen another UNTED STATES PATENTS exchanger begins its regenerationcycle. 1.893.933 [H933 Dotterweich 210/96 6 Claims, 5 Drawing FiguresMULTI-TANK ION EXCHANGE WATER TREATMENT SYSTEM BACKGROUND OF THEINVENTION This invention relates to an ion exchange water treatmentsystem of the type in which two or more ion ex changers are connected inparallel in a water system so as to provide relatively large treatmentcapacity while keeping water service available to the using system whenone of the exchangers is in its regeneration cycle.

SUMMARY OF THE INVENTION The general aim of the present invention is tointerconnect the exchangers with unique and relatively simple means fortaking each exchanger out of service when the exchanger begins itsregenerating cycle, for keeping the exchanger out of service and in astandby status after such exchanger completes its regenerating cycle.and for bringing the standby exchanger back into service when anotherexchanger begins its regenerating cycle.

Another object is to provide novel interconnecting means which enableconstruction of the exchangers as virtually identical modular units andwhich enable a given exchanger to be used interchangeably in treat mentsystems equipped with two. three or even more exchangers.

The invention also resides in the provision of unique hydraulicinterconnecting means which switch a newly regenerating exchanger out ofservice and which switch a standby exchanger into service in response tothe initial flow of liquid through the drain line of the newlyregenerating exchanger.

These and other objects and advantages of the invention will become moreapparent from the following detailed description when taken inconjunction with the accompanying drawingsv BRIEF DESCRIPTION OF THEDRAWINGS FIG. I is a schematic view and fluid circuit diagram of a newand improved ion exchange water treatment system embodying the novelfeatures of the present invention.

FIG. 2 is a diagram of the electric control circuit for the treatmentsystem shown in FIG. 1.

FIG. 3 is a schematic view of an alternative fluid circuit.

FIGS. 4 and 5 are views similar to FIG. 3 but showing differentconditions of the fluid circuit illustrated in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in thedrawings for purposes of illustration, the invention is embodied in anion exchange water treatment system having a plurality of ion exchangersII] which are connected in parallel in a water system to treat raw waterflowing from a supply line I] and to deliver treated water into aservice line 13 and then to at using system. Herein. three exchangersltlut [0b and I00 are shown as being connected into the water sys temalthough more than three exchangers could be used and. in manyinstances. only two exchangers will be employed. With two or moreexchangers connected in parallel. a relatively large supply of treatedwater is made available to the using system and. in addition. the

supply of water to the using system is not interrupted when one oftheexchangers is being regenerated. Thus. a muIti-exchanger treatmentsystem of the type disclosed herein is capable of serving a large usingsystem more adequately than would be the case if only a single exchangerwere employed.

The basic exchangers 10 are of well known construc tion and eachincludes a tank I4 containing a bed 15 of ion exchange resin. Waterflows into the top of each tank through an inlet line I6 communicatingwith the supply line I I, flows downwardly through the resin bed fortreatment, and then flows out of the bottom of the tank through anoutlet line 17 communicating with the service line I3.

When the exchangers 10 are regenerated to recondi tion the resin beds15. water and regenerating chemi cals flow into and out of the tanksthrough riser pipes 19. the liquid which flows out each tank beingcarried to a drain by a drain line 20 having a flow controller 21 forrestricting the rate of flow. The flow through each riser pipe iscontrolled by a regenerating valve 23 (FIG. 2) driven by an electricallyenergized valve motor 24 which. in turn. is controlled by anelectrically energized timing motor 25. To simplify the drawings. thevalve and the two motors have not been illustrated in detail but insteadhave been schematically shown as incorporated in a regeneration controlunit 26 (FIGS. I and 2) located at the top of the tank [4. Various typesofconventional regeneration control units may be used and. since thebasic construction. organization and operation of such units are wellknown. these details do not require description here. It will suffice tosay that the timing motor of the unit used in the present instance isenergized when a sensor 27 (FIGS. 1 and 2) detects the need forregeneration and. once energized. the tim ing motor causes the exchangerto operate through a complete regeneration cycle.

In the present instance the exchangers II] are interlocked to preventmore than one exchanger from regenerating at a time, the interlockingbeing achieved in a relatively simple and versatile manner and enablingany number of exchangers to be installed in the water system withoutincreasing the complexity of the interlocking hardware. Such simplicityand versatility are achieved by disabling the sensor 27 of eachexchanger whenever any other exchanger is regenerating so that suchsensor is incapable of initiating a regeneration cycle even thoughregeneration may be required.

In one specific embodiment the control units 26 of the exchangers I0 areconnected into a control circuit 30 (FIG. 2) having lines L-I and L2connected across a source of voltage such as volts a.c. The circuit 30includes three control branches 3] connected in parallel combinationwith one another across the lines L-l and L-2, there being one controlunit 26 connected within and adapted to be energized by way of eachcontrol branch. The the circuit 30 further comprises three energizingpaths 33 which are connected in parallel combination with one anotherand which include means for energizing the sensors 27. Herein, thesemeans have been shown as being transformers 34 having their primarycoils connected into the respective energizing paths 33 and adapted toconvert the 120 volts a.c. source voltage into 24 volts d.c. forenergizing the sensors 27.

The sensor 27 for each exchanger I0 is attached to the riser pipe 19(FIG. 1) and has been illustrated in a schematic manner since the sensorwhich is used herein is well known and since various types of sensorsmay be used. Basically. the sensor which is disclosed detects theconductivity of the resin bed and produces an electrical signal as anincident to the conductivity reaching a certain level when the bedrequires regenerating. The sensor is adapted to be energized by way of asensing circuit 35 (FIG. 2) and has been illustrated schematically asforming part of a Wheatstone bridge 36 which is normally in balance butwhich reaches a critical level of imbalance when the conductivity of theresin bed changes sufficiently to dictate the need for regeneration. Toenergize the sensors 27. the secondary coils of the transformers 34 areincluded within the respective sensing circuits 35 and are connected tothe input terminals of the respective bridge 36. The output terminals ofeach bridge 36 are connected across a responding means in the form of anormally de-energized relay 37 whose normally open contacts 39 7 arelocated in the respective control branch 31 of the control circuit 30.

Let it be assumed that none of the exchangers 10 is in a regenerationcycle and that the sensor 27 of one exchanger (for example. theexchanger 10a) detects that such exchanger requires regeneration. Atsuch time. the bridge 36a reaches a critical level of imbalance andsupplies the relay 37a with current sufficiently high to energize therelay. Energization of the relay causes closing of the contacts 390 inthe control branch 31a so as to energize the timing motor of the controlunit 26a. As the timing motor starts up. a cam [not shown) driven by themotor closes a normally open switch 40a which seals around the relaycontacts 39a and maintains an energizing circuit to the motor when therelay 37a is subsequently de-energized and the relay contacts re-opened.As will be explained subsequently. the relay 37a is de-energized shortlyafter the initiation of a regenerating cycle.

After being energized. the timing motor 25a acts through conventionalmechanism and circuitry housed within the control unit 26a andillustrated schematically at 4111 (FIG. 2) to cause energization of thevalve motor 24a at appropriate intervals. The valve motor drives theregenerating valve 230 to different positions to cause the exchanger 10ato operate through a full re generation cycle. When the regenerationcycle is completed and the valve 23a is returned to service position.the timing motor 25:: causes opening of the switch 40a to de-energizethe control branch 310.

To advantage the exchangers 10 are interlocked against simultaneousregeneration by three normally closed interlocking switches 43a. 43b and43c connected with one another in the control circuit 30 in a seriescombination which. in turn. is connected in series with the parallelcombination of energizing paths 33. If any one of the interlockingswitches 43 is opened. current flow to all of the energizing paths 33 isinterrupted and thus the transformers 34 and the sensing circuits 35 arede-energized. Under these conditions. any exchanger which is not alreadyregenerating cannot begin a regeneration cycle because. even iftheconductivity of the resin bed 15 of such exchanger reaches theregeneration level. the respective sensing circuit 35 is de-energizedand thus the relay 37 cannot be ener gized to close the contacts 39 inthe respective control branch 31.

Again. let it be assumed that none of the exchangers 10 is in aregeneration cycle and that the sensor 27 of one exchanger (theexchanger 10a) detects that such exchanger requires regeneration. Whenthe previously described regeneration cycle is initiated and the valvemotor 240 is energized. a cam 44a (FIG. 2) driven by the valve motorcauses the interlocking switch 43a to open. As a result. all of thetransformers 34 and sensing circuits 35 are de-energized since currentflow to the energizing paths 33 is interrupted. Thus. the other twoexchangers 10b and 10c cannot begin a regeneration cycle. Even thoughthe relay 37a is de-energized when the switch 43a is opened. theexchanger 10a continues with its regeneration cycle by virtue of thecircuit maintained to the control branch 310 by the sealing switch 40a.

The interlocking switch 430 is held open during the entire regeneratingcycle of the exchanger 10a and thus the exchangers 10b and are preventedfrom regenerating. When the exchanger 10a completes its regenerationcycle. the cam 44a closes the interlocking switch 430 to re-establishcurrent flow to all of the energizing paths 33 so that any exchangerwhich either then or subsequently requires regeneration is capable ofbeginning its regenerating cycle. It will be appreciated that theinterlocking switches 43b and 430 are' opened and closed in the samefashion as the interlock ing switch 43a and thus the exchangers 10a andH]:- are prevented from regenerating when the exchanger 10b isregenerating and the exchangers 10a and [0b are prevented fromregenerating when the exchanger 100 is regenerating.

From the foregoing, it will be apparent that the energizing paths 33 forthe sensor circuits 35 are connected in parallel combination with oneanother and are separated or isolated from the parallel combination ofthe control branches 31. The interlocking switches 43 for controllingthe energizing paths 33 are connected in a series combination which isconnected in series with the parallel combination of energizing paths.With this arrangement. the circuitry is relatively simple and isvirtually identical for each exchanger 10 so as to enable manufacture ofthe exchangers as substantially identical modular units. ln addition.any number of exchangers may be added to the water treatment system andinterlocked with the other exchangers without increasing the complexityof the wiring harnesses between the exchangers. For example. it will beseen in FIG. 2 that the exchanger 10a is connected to the exchanger 10bby a four-wire harness not including a ground wire) and by ajack andplug unit 45a (the latter being shown in four places in the drawing butcollectively being one unit). The exchanger 10b. in turn. is connectedto the exchanger l0c by a similar four-wire harness and jack and plugunit 45b. Any number of exchangers may be connected into the system withsimilar four-wire harnesses and without need of providing additionalwiring within the harnesses. The lead exchanger 10a. of course. includesan additional harness leading to the ac. voltage source. and the jack451' of the harness of the final exchanger 100 is suitably jumpered asindicated at 46 in order to complete the control circuit 30.

According to the present invention. the exchangers 10 are hydraulicallyinterconnected in a novel manner so that each exchanger which completesits regenerating cycle is not immediately returned to service use butinstead is held in a reserve or standby status until such time asanother exchanger begins its regenerating cy cle. In this way, a freshlyregenerated exchanger is made available to the using system wheneveranother exchanger begins regenerating and thus a continuous supply oftreated water is insured.

In order to prevent a given exchanger from returning to service useafter it completes its regenerating cycle. the flow system through theexchanger is closed off during the regenerating cycle and is kept closeduntil another exchanger beings regeneration. To close off the flowsystem. shutoff valves and 51 (FIG. 1) are connected into the inlet andoutlet lines 16 and 17 of each exchanger and are adapted to be movedbetween opened and closed positions by fluid-operated actuators 53 and54. In this instance. cach valve actuator comprises a walled chamber 55which is divided into two compartments by a flexible diaphragm 56. thelatter being springbiased in an upward direction and being connected tothe shut-off valve. When fluid under pres sure is admitted into theupper side of the chamber 55 of the upper actuator 53 through a line 57the respective diaphragm is flexed downwardly to close off the valve 50in the inlet line 16. At the same time. pressure is transmitted to theupper side of the chamber of the lower actuator 54 through a line 59 andserves to close off the valve in the outlet line 17. When the pressureis dumped from the line 57. both valves are automatically returned totheir open positions by virtue of the upward spring bias applied to thediaphragms 56.

To control the flow of pressure fluid to and from the valve actuators 53and 54. a pilot valve 60 is associated with each exchanger 10 andincludes a valve spool 61 slidable within a housing 63. When the valvespool is shifted to the right from the position shown in FIG. 1, a land64 is located so as to enable the line 57 to communicate with a line 65connected to the supply line 11. Accordingly, water under pressure isdirected to the actuators 53 and 54 to close the shut-off valves 50 and51. When the spool 61 is returned to the left, the line 57 communicateswith a drain line 66 and thus the water is dumped from the actuators toallow the shutoff valves to return to their open positions.

Normally. the valve spool 61 of each pilot valve 60 is located to theleft in a service position as shown in FIG. 1. When the associatedexchanger 10 begins its regenerating cycle. the valve spool is shiftedto the right to a standby position to close off the flow system of theexchanger and thus take the exchanger out of service use. To shift thevalve spool from its service position to its standby position. a line 67advantageously communicates with the exchanger drain line 20 at a pointupstream from the flow controller 2] and also communicates with achamber 69 located at the left end of the valve housing 63, there beinga piston 70 slidable in the chamber and connected to the valve spool 61.When the exchanger begins its regenerating cycle. liquid flows throughthe drain line 20 and. because of the restriction created by the flowcontroller 21, a pressure pulse is created in the line 67 and istransmitted to the piston 70 to shift the valve spool 61 to the right toits standby position. Thus, the shut-off valves 50 and 51 are closedautomatically as an incident to the exchanger producing a pressure pulsein its drain line 20 at the beginning of its regenerating cycle.

The spool 61 of a given pilot valve 60 remains in its standby positioneven after the associated exchanger 10 completes its regenerating cycleand is returned to service position only when another exchanger beginsregeneration. To return the spool to its service position. a pressurepulse is transmitted to a piston connected to the right end of the valvespool and slidable within a chamber 76 at the right end of the valvehousing 63. The chamber 76 communicates with a header 77 which. in turn.communicates with the drain lines 20 of the other two exchangers by wayof lines 79 and 80. Thus. when either of the other two exchangers 10begins a regeneration cycle, a pressure pulse from one of the drainlines 20 is transmitted through the lines 79 or 80 to the piston 75 ofthe valve spool 61 in standby position. The spool thus is shifted to theleft to its service position by the pressure pulse so as to causeopening of the shut-off valves 50 and 51 of the associated ex changerand thereby switch the exchanger from standby to service.

From the foregoing. it will be apparent that two functions are performedby the pressure pulse produced in the drain line 20 of any givenexchanger 10 when that exchanger begins its regeneration cycle. That is.the pressure pulse shifts the valve spool 61 of the regeneratingexchanger into its standby position so that the ex changer will notreturn to service when its regenerating cycle is completed. Secondly.the pressure pulse simultaneously acts on the valve spool of theexchanger which has previously been on standby and shifts that valvespool to its service position so as to switch the as sociated exchangerfrom standby to service. In this way. a freshly regenerated exchanger isbrought into service each time another exchanger begins its regenerationcycle. Since the exchangers are electrically interlocked againstsimultaneous regeneration. it is not possible for a pressure pulse toexist in more than one drain line 20 at any given time. Accordingly.when pressure is applied to one of the pistons 70 or 76 of any valvespool. there is no back pressure against the other piston and thus thespool may shift freely. Moreover. once shifted. the valve spool remainsin a stable position until it is shifted reversely by a pressure pulseoriginating from another exchanger.

An alternative pilot valve arrangement is shown in FIGS. 3 to 5 and isadvantageous in that it reduces the number of pilot valves required andalso simplifies the piping so as to enable additional exchangers to beeasily added to the system without need of directly connecting the drainline of each exchanger to the pilot valve of every other exchanger. Whenthree exchangers 10 are connected in the system, two pilot valves and 91are used and the valves include spools 93 and 94, re spectively,disposed end-to-end and each adapted to move between left and rightpositions.

As shown. the line 67a leads to the left end of the spool 93, the line67c leads to the right end of the spool 94, and the line 67b leads to apipe 95 which extends between the right end of the spool 93 and the leftend of the spool 94. The supply line 11 and the line 57a lead to thevalve 90 while the lines 57b and 57c lead to the valve 91. The valve 90communicates directly with a drain line 96 while the valve 91communicates with the drain line by way of lines 97 and 98. Finally, thevalve 90 communicates with the valve 91 via lines 99 and FIG. 3 showsthe positions of the valve spools 93 and 94 when the exchanger 10a isregenerating and the exchangers 10b and 10c are in service. When theexchanger 100 begins regenerating, a pressure pulse is produced in theline 67a to shift the spool 93 to the right to the position shown inFIG. 3. As a result. water under pressure is directed from the supplyline 11 to the line 57a to close off the flow system of the exchanger10a.

Now assume that the exchanger 10a completes re generation and theexchanger 10b begins regenerating. At this time. a pressure pulse isproduced in the line 67b and passes through the pipe 95 to shift thespool 93 to the left to the position shown in FIG. 4. As a resalt. theline 5711 is vented to the drain line 96 to cause opening of the llowsystem of the exchanger I01! so as to switch that exchanger from standbyto service. At the same time. water under pressure is directed from thesupply line ll to the line 5711 via the line 99 and thus the flow systemofthe exchanger 10!) is closed off.

If it now be assumed that the exchanger lllb completes regeneration andthe exchanger 10c begins re generation. a pressure pulse is produced inthe line 67c to shift the spool 94 to the left as shown in FIG. 5. As anincident thereto. the line 57b is vented to the drain line 96 by way ofthe line 97 and thus the flow system of the exchanger 10/1 is opened upto switch that exchanger from standby to service. In addition. waterunder pressure is directed from the supply line 1] to the line 571 byway of the line 99 and thus the flow system of the exchanger 100 isclosed off.

if the exchanger Illa is the exchanger which next regenerates. the spool93 is shifted to the right and the line 570 is vented to the drain line96 so as to return the exchanger 101 to service use. If the exchanger10b is the exchanger which next regenerates. the pressure pulse producedin the line 67b and the pipe 95 shifts the spool 94 to the right so thatthe line 57c is vented to the drain line 96 by way of the line 98.

Ifthe exchangers l regenerate in certain unusual sequences. the pressurepulses alone are not effective to shift the valve spools 93 and 94 tothe proper positions To overcome this disability. a rod 101 is looselytelescoped into the pipe 95. The length of the rod is equal to thedistance between adjacent ends of the spools when the spool 93 is leftand the spool 94 is right. minus the distance through which a spoolshifts in moving between its positions.

Now assume. for example. that the exchanger a is in standby (the spool93 thus being to the right] and the exchanger [0c begins regenerating.The pressure pulse produced in the line 67c is effective to move thespool 94 from right to left but, without the rod 101. the spool 93 wouldremain to the right. Water under pressure then would continue to bedirected from the supply line 11 to the line 57a and none would bedirected to the line 570. By virtue of the intermediate rod I01, however. the spool 94 mechanically shifts the spool 93 to the left. theleft end of the spool 94 engaging and pushing the rod which. in turn.engages and pushes the spool 93. The spools thus are positioned as shownin FIG. 3 to switch the exchanger 10a to service and to place theexchanger 10c in standby. The rod I01 thus causes the spool 93 to shiftleft [if that spool is right) when the spool 94 shifts left and yetleaves the spool 94 free to shift right without changing the position ofthe spool 93. With this arrangement. the exchangers will always beproperly placed into and taken out of standby regardless of the sequenceof regeneration.

From the foregoing. it will be apparent that the valving arrangementshown in FIGS. 3 to 5 enables three exchangers to be controlled withonly two pilot valves and 91. I have found that as many as twelveexchangers can be incorporated in the system and. for each exchangerthat is added. one additional pilot valve is used. Thus, the number ofpilot valves is one less than the number of exchangers. In addition toreducing the number of pilot valves. the valving arrangement shown inFIGS. 3 to 5 simplifies the piping between the exchangers and enablesadditional exchangers to be easily incorporated into the system.

I claim:

I. An ion exchange water treatment system comprising a plurality of ionexchangers connected in parallel in a water system. each of saidexchangers having a flow system by which water flows through theexchanger when the latter is in service use. valve means associated withthe flow system of each exchanger and movable between open and closedpositions to open and close such flow system. means associated with eachexchanger for intermittently causing the exchanger to operate through aregenerating cycle, each exchanger including a drain system throughwhich liquid flows during said regenerating cycle. and means associatedwith each exchanger and operable to cause closing of the valve means ofsuch exchanger and to cause opening of the closed valve means of anyother exchanger in response to the flow of liquid through the drainsystem of such exchanger.

2. An ion exchange water treatment system comprising a plurality of ionexchangers connected in parallel in a water system, each of saidexchangers having a flow system by which water flows through the exchanger when the latter is in service use, at least one valve associatedwith the flow system of each exchanger and movable between open andclosed positions to open and close such flow system. a fluid operatedactuator connected to each valve for moving the latter between itspositions as fluid is delivered to and dumped from the actuator. a pilotvalve associated with each actuator and movable between service andstandby positions. said pilot valve delivering fluid to said actuatorwhen in one of said positions and dumping fluid from the actuator whenin the other of said positions, means associated with each exchanger forintermittently causing the exchanger to operate through a regeneratingcycle. each exchanger including a drain system through which liquidflows during said regenerating cycle, and means connecting the drainsystem of each exchanger with the pilot valve of such exchanger and withthe pilot valve of every other exchanger to cause the respective pilotvalve to move to standby positions and to cause any other pilot valve instandby po sition to move to service position in response to the flow ofliquid through the drain system of such exchanger.

3. An ion exchange water treatment system as defined in claim 2 in whichat least three ion exchangers are connected in parallel in said watersystem.

4. An ion exchange water treatment system comprising a plurality of ionexchangers connected in parallel in a water system. each of saidexchangers having a flow system by which water flows through theexchanger when the latter is in service use. at least one valveassociated with the flow system of each exchanger and movable betweenopen and closed positions to open and close such flow system. a fluidoperated actuator connected to each valve for moving the latter betweenits positions as fluid is delivered to and dumped from the actuator. aplurality of pilot valves associated with said exchangers andcontrolling the flow of fluid to and from said actuators, meansassociated with each exchanger for intermittently causing the exchangerto operate through a regenerating cycle. each exchanger including adrain system through which liquid flows during said regenerating cycle.and means connecting the drain systems of said exchangers with saidpilot valves to cause the pilot valves to effect closing of the flowsystem of any regenerating exchanger and opening of the closed flowsystem of any other exchanger in response to the flow of liquid throughthe drain system of said regenerating exchanger.

LII

5. An ion exchange water treatment system as defined in claim 4 in whichthe number of pilot valves is one less than the number of exchangers.

6. An ion exchange water treatment system as defined in claim 5 whichincludes at least two pilot valves disposed end-to-end. each of saidvalves including a spool movable between first and second positions. andmeans mechanically interconnecting said spools to shift one of thespools from its first position to its second position when the otherspool is shifted from its first position to its second position whileleaving said other spool free to shift back to its first positionwithout changing the position of said one spool.

1. An ion exchange water treatment system comprising a plurality of ionexchangers connected in parallel in a water system, each of saidexchangers having a flow system by which water flows through theexchanger when the latter is in service use, valve means associated withthe flow system of each exchanger and movable between open and closedpositions to open and close such flow system, means associated with eachexchanger for intermittently causing the exchanger to operate through aregenerating cycle, each exchanger including a drain system throughwhich liquid flows during said regenerating cycle, and means associatedwith each exchanger and operable to cause closing of the valve means ofsuch exchanger and to cause opening of the closed valve means of anyother exchanger in response to the flow of liquid through the drainsystem of such exchanger.
 2. An ion exchange water treatment systemcomprising a plurality of ion exchangers connected in parallel in awater system, each of said exchangers having a flow system by whichwater flows through the exchanger when the latter is in service use, atleast one valve associated with the flow system of each exchanger andmovable between open and closed positions to open and close such flowsystem, a fluid operated actuator connected to each valve for moving thelatter between its positions as fluid is delivered to and dumped fromthe actuator, a pilot valve associated with each actuator and movablebetween service and standby positions, said pilot valve delivering fluidto said actuator when in one of said positions and dumping fluid fromthe actuator when in the other of said positions, means associated witheach exchanger for intermittently causing the exchanger to operatethrough a regenerating cycle, each exchanger including a drain systemthrough which liquid flows during said regenerating cycle, and meansconnecting the drain system of each exchanger with the pilot valve ofsuch exchanger and with the pilot valve of every other exchanger tocause the respective pilot valve to move to standby positions and tocause any other pilot valve in standby position to move to serviceposition in response to the flow of liquid through the drain system ofsuch exchanger.
 3. An ion exchange water treatment system as defined inclaim 2 in which at least three ion exchangers are connected in parallelin said water system.
 4. An ion exchange water treatment systemcomprising a plurality of ion exchangers connected in parallel in awater system, each of said exchangers having a flow system by whichwater flows through the exchanger when the latter is in service use, atleast one valve associated with the flow system of each exchanger andmovable between open and closed positions to open and close such flowsystem, a fluid operated actuator connected to each valve for moving thelatter between its positions as fluid is delivered to and dumped fromthe actuator, a plurality of pilot valves associated with saidexchangers and controlling the flow of fluid to and from said actuators,means associated with each exchanger for intermittently causing theexchanger to operate through a regenerating cycle, each exchangerincluding a drain system through which liquid flows during saidregenerating cycle, and means connecting the drain systems of saidexchangers with said pilot valves to cause the pilot valves to effectclosing of the flow system of any regenerating exchanger and opening ofthe closed flow system of any other exchanger in response to the flow ofliquid through the drain system of said regenerating exchanger.
 5. Anion exchange water treatment system as defined in claim 4 in which thenumber of pilot valves is one less than the number of exchangers.
 6. Anion exchange water treatment system as defined in claim 5 which includesat least two pilot valves disposed end-to-end, each of said valvesincluding a spool movable between first and second positions, and meansmechanically interconnecting said spools to shift one of the spools fromits first position to its second position when the other spool isshifted from its first position to its second position while leavingsaid other spool free to shift back to its first position withoutchanging the position of said one spool.